Self-Q-switched and multicolor operation of a Tm:LuAG laser

In this paper, we report self-Q-switched (SQS) and three-color operation of an all-solid-state Tm:LuAG laser for the first time to our knowledge. In the experiments, a low-cost 3 W AlGaAs laser diode was used to end-pump the Tm:LuAG crystal inside a four-mirror x cavity. In typical continuous-wave (cw) operation, as high as 754 mW output power was obtained with 49% power efficiency at 2023 nm. Three-color and SQS operations were initiated by fine tuning of the curved mirror separation within the stability range of the resonator. In the three-color regime, the Tm:LuAG laser produced two extra, i.e., 2019 and 2033 nm, wavelength oscillations in addition to on at 2023 nm. As high as 542 mW output power was observed in this regime. To the best of our knowledge, this is the first stable three-color laser operation obtained with an isotropic gain medium without having any birefringent elements in the cavity. Furthermore, the SQS operations were also observed at other curved mirror separations. In the SQS regime, the Tm:LuAG laser produced as fast as 13.3 kHz repetition rate pulses and as high as 42.5 µJ pulse energy. Analysis of power-dependent repetition rate data gave an estimated value of 2% for the round-trip saturable loss of the crystal. As far as we know, this is the first cw-pumped stable SQS 2 µm laser that contains an ordered isotropic gain medium as well as the highest pulse energy obtained in any cw-pumped SQS laser.